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The Debate on Canine Domestication
Canine Origin Story
Jawbone and teeth fragments held at the Oxford Museum of Natural History. DNA extracted from these and similar materials contributes to the effort to track the separation between wolf and dog.

Researchers have identified the origin of cattle, horses, pigs, sheep, camels, ducks, chickens, cats and goats. But the genesis of the domestic dog, our oldest companion and the most varied, numerous and widely distributed domestic animal on the globe? We’re still trying to figure out that one.

The study of patterns of diversity is called systematics, and it is a critical subdivision of evolutionary biology. Systematics researchers (earlier called naturalists and taxonomists) sort out species’ genealogical relationships and estimate the points at which populations diverged from one another. Traditionally, they relied on observations of differences in stable physical traits like teeth, skulls and sometimes fossils. More recently, genome-wide comparisons have been used to provide detailed information about species relationships, including the question of when and where wolves became dogs.

Canis lupus familiaris exhibits the most variability in shape, size, behavior and temperament of any mammal species living on earth. About one billion dogs, a population larger than any other domestic subspecies, roam the globe. Canine fossils, some dating to as long ago as 36,000 years, are found on every continent except Antarctica.

Add to that the unusual phenomenon that extreme variation can occur in as little as one generation—a sort of evolution at hyper speed—and we begin to understand why classifying domestic dogs has challenged many of the taxonomical systems that have been used to make sense of Canidae, a family that includes wolves, jackals, foxes and dogs.

Science Evolves

Historically, as far back as the fourth century BCE, theories of the descent of animals were the product of using philosophical approaches to relate organic life to the history of time. At first, fundamental ideas about species-change involved sorting out living beings by means of their common essential properties. Philosophers wanted to know how organic life forms were related, not where they came from.

The Greek philosopher Aristotle (384–322 BCE) endorsed the idea that natural beings were always here and always would be. He commented on the dog’s origin, not in respect to the animal’s continuous chronological past but rather, in terms of breed creation. In his view, the dog that nature created was bred to the fox to make small dogs and to bears to make big ones, perhaps making the point that breeds (although he was mistaken about cross-species hybridization) were created by humans. Still, in the Aristotelian view, dogs always existed.

As time went on, the earliest naturalists came to understand that species were related in more complicated ways, and began to devise orderly classification systems. The bigger picture of life, however, was explained within a theological context: a specific act of an omnipotent creator transformed all living things whole and complete. The revolutionary notion that every animal might not be a singular divine creation didn’t materialize until the late Middle Ages, a contradiction that had to be explored hypothetically to avoid conflict with religious doctrine.

In the late 18th century, France’s leading naturalist and the father of paleontology, Georges Cuvier (1769–1832), introduced a new way of looking at life and death. Although he was firmly in the camp of divine creationism, he theorized that animals eventually went extinct.

Earlier, 16th-century English cleric Edward Topsell (1572–1625), author of The History of Four-footed Beasts, whose worldview was defined by fire-and-brimstone religion, based his categories on morality. This was not as much of a stretch as it might seem from today’s vantage point; during Topsell’s time, people had real reason to fear wolves. For them, the predatory wolf and sagacious, noble dog provided excellent examples of two moral extremes.

Domesticated farm livestock had derived from prey species, and no other large predator had (or has) been domesticated. So it seemed illogical that the gentle, devoted dog could have evolved from the wolf. As one writer lamented, “How could such a noble animal as the dog be derived from the likes of the wolf? If evolution were true of dogs and wolves, wouldn’t every beast choose to live the noble life?” Indeed.

But as Darwin later observed, if organic beings didn’t possess an inherent tendency to vary, humans could do nothing. Unlike bears and lions, wolves, for reasons still scientifically unclear, possessed the variation necessary for the creation of the multiple hundreds of dog breeds recognized today.

The Shape of Things

Imagine how frustrating it must have been to try to make sense of how dogs were related and where they came from based on their appearance. Travel the world over and a cat will usually look like a cat, but dogs were a vexing contradiction.

The lack of understanding of the complexity of canine morphology made it difficult to unravel relationships among the ever-increasing numbers of dogs and dog-like animals being discovered on far-away, previously unexplored continents. In the Americas, many were likely Old World breeds introduced by European explorers, eventually returned to a feral state. Over time, they interbred with American Indian dogs, wolves and coyotes, defaulting to pariah-type dogs—a catchall term for semi-feral, free-ranging canines. But a misunderstanding of the distinct differences between wild, tame, domestic and feral dogs added to the confusion about how Canidae should be classified.

The father of modern taxonomy, Carl Linnaeus (1707–1778), assigned dogs both wild and domestic to groups based on their anatomy (muzzle, jaw, ear shape), tail carriage (dog tails curve when relaxed, wolf tails don’t), hair texture, limb length and behavior, criteria that are still used today.

Linnaeus’s contemporary, Georges- Louis Leclerc, Comte de Buffon (1707– 1788)—of whom Linnaeus sniffed, “Always eloquent, often incorrect”— suspected that changes in canine morphology were influenced by environmental pressures, such as climate. But, like his colleagues, Buffon did not consider change within an evolutionary context.

Dividing dogs into categories based on skull shape was Cuvier’s idea, and although his forward-thinking approach to paleontology and the history of organisms would seem to make him an advocate for evolution, he was not. Cuvier’s interest, after all, was in a species’ demise, not its origin. Nevertheless, his contributions greatly influenced Charles Darwin.

Darwin (1809–1882) believed that the dog had multiple origins: from wolves, jackals and at least one South American species. He supported the latter by referencing his observations of dogs in Patagonia who swam underwater and an unusual dog he had seen in Central America. He also advanced the idea of multi-regional domestication.

Darwin further imagined that these small populations of “inferior” native dogs were eventually supplanted by the incursion of more robust dogs introduced by Europeans, an analogy he used to demonstrate the idea of “survival of the fittest.”

Although the fundamental theory of origin is attributed to Darwin, other taxonomists previously proposed similar ideas and connections, including Jean-Baptiste Lamarck and Alfred Russel Wallace. Unlike Lamarck and Wallace, however, Darwin suggested that the evolutionary process occurred through natural selection.

Although Darwin used the breeding of dogs and other artificially selected animals as analogies to explain how natural selection worked, dogs continued to be an untidy group of animals —a puzzle that science has began to unlock by the use of genome-wide sequencing.

In the Genes

Once scientists discovered methods to explore origin at the molecular level, they began to test these historical theories. As early as the 1970s, research papers were published suggesting that dogs may have been derived from several different gray wolf populations, and that canine domestication may have happened much earlier than the fossil record’s 15,000 years ago. By the late 1990s, geneticists worldwide were working together to build a comprehensive map that would chart the evolutionary journey of domestic dogs.

The path was not smooth. Differences of opinion erupted and criticism of research methodologies undermined a delicately balanced collaboration process. Numerous studies argued for canine origin in places as diverse as East Asia, Mongolia, Siberia, Europe and Africa, with timing varying from somewhere between 15,000 and 135,000 years ago. Archeologists who’d studied ancient canine burials were relegated to the sidelines, their fossil records dismissed as “old school,” which created further dissention. Researchers struggled to find common ground, but without much success.

The debate ramped up in 2013, when UCLA evolutionary biologist Robert Wayne and his team published a comprehensive set of data suggesting that dogs evolved from a group of European wolves, now extinct, somewhere between 19,000 and 32,000 years ago.

Two years later, Peter Savolainen, a molecular biologist, and his colleagues at the Royal Institute of Technology in Stockholm published convincing results indicating that dogs originated in China, south of the Yangtze River. They estimated that this dog population split from wolves 33,000 years ago.

Both teams were sequencing DNA. Why were their findings literally all over the map?

Savolainen’s research team analyzed DNA samples from living global dog and wolf populations, then tracked DNA from least to most diverse, going back through time. The general rule is that the older a population of animals, the more diversity it has in its genome, which is a hallmark of ancient origin.

Whether these animals represented the first domesticated dogs or, rather, dogs who migrated to the region from elsewhere and split off from a more ancient dog population, is unresolved. Fossil remains of an ancestral and probably extinct population of wolves that would have been indigenous to the area would seal the deal, but researchers have yet to find them. As Savolainen notes, “We have access to some archaeological samples we are about to analyze. However, there has been quite little archaeological work, especially on animals, in the region.”

While Savolainen and his colleagues worked backward in time, Wayne’s group worked forward, tracking ancient DNA collected from prehistoric bones of wolves and wolf-like dogs, then measuring decreasing genetic diversity. As DNA becomes less diverse, it points to animals transitioning from wolves to dogs. A dead end indicates that a lineage became extinct in that particular region.

Wayne’s team sequenced ancient DNA on canid skulls and bone fragments discovered in present-day Siberia and the Czech Republic dating to between 27,000 and 33,000 years ago. The physical characteristics of the skulls—wider muzzles and foreshortened jaws—suggest that these were ancient proto-dogs, not wolves. The canids may have looked similar to today’s Arctic breeds (for example, the Siberian Husky and the Greenland Dog), but were probably much larger. Although their findings were met with skepticism, the team said their data showed that domestic dogs originated from different wolf populations at different times in different places, in a series of starts and stops. And, they added, living dogs are more closely related to ancient extinct wolves than they are to modern wolves.

In an interesting twist, Wayne’s findings reignited the theory of parallel and multi-regional proto-domestication, an idea that Darwin introduced in the 19th century and one that’s gone in and out of favor since.

Both studies have detractors. Some claim that diversity in Savolainen’s ancient dog population is a result of admixture with European dogs as people traversed the Silk Road. Those who criticize Wayne’s study maintain that he has no solid proof that the ancient bones he’s studying are definitively wolf or dog. Additionally, critics say, his study is geographically biased because he excluded samples from dogs in China based on his position that there are no ancient dogs there.

Although the two studies point in very different directions, Savolainen and Wayne may both be right. It’s possible that dogs were domesticated multiple times in different regions, and that most lineages died out when humans were faced with overwhelming challenges, like climate change. Their findings aren’t mutually exclusive.

Crunching the (Very Big) Numbers

One reason for the disparities, according to Oxford’s visionary evolutionary biologist Greger Larson, who was a part of a team that successfully mapped the origin of the pig, is that scientists studying the dog are not including enough ancient DNA in their studies.

Larson and colleague Keith Dobney, an archaeologist at the University of Aberdeen, had the idea to bring together all the evidence collected to date, find ancient canid specimens from museums, apply state-of-the-art technology and create a database bigger than anything produced before. All they had to do was convince scientists to agree to work together.

Fortunately for canine genetics, Larson was able to sell the idea that more cooperation and collaboration improves the outcome. As chief mediator and conciliator, and supported by substantial funding, he has persuaded more than 50 influential canine evolutionary scientists to join the project. Team members include archaeologists, paleobiologists, anthropologists, zooarchaeologists, paleogeologists and others.

The purpose of the study, which began in 2013 and is slated to wrap up this year, is to combine ancient DNA analysis and geometric morphometric techniques and apply them to archaeological canid remains. This, he suggests, will directly address where, when and how many times dogs were domesticated.

Geometric morphometrics, the study of form in two or three dimensions, is a powerful new way to visually quantify evolutionary relationships. It does this by correlating thousands of geometric points that identify exact places on bones—specifically, points of evolutionary significance that differ between very closely related animals such as the wolf and the dog.

Using a special camera, researchers take hundreds of 360-degree photographs. Software then transfers the pictures to a three-dimensional computerized image that emphasizes a set of tightly defined, very specific points on each bone. The process results in holographic- like images that show domestication in progress through space and time, much like a movie.

Additionally, scientists are isolating and examining ancient DNA collected from museum specimens, looking for changes in the degree of genetic diversity over long periods. This will provide a comprehensive overview of the wolf-to-dog transition from the beginning to the present.

No individual genetic fragment of DNA says This is a wolf or This is a dog. Rather, scientists tease the two apart by looking at strands of DNA and identifying and measuring similarities and differences. As differences become more extreme, the separation between wolf, proto-dog and, finally, dog is suggested.

The team hopes to isolate genetic fragments that can be linked to minor changes in the geometric morphometricimaged samples. Combining the two techniques will tell a deeper, more layered and detailed story about canine domestication.

Larson expects to analyze up to 7,000 specimens representing wolves, incipient canids and domestic dogs. “We’re taking samples from all over the world, sources in not only museums but from private collections, too. Curators are very agreeable when we ask for permission, and they’re usually very happy to have us take photos and DNA samples. They help us, and in turn, we provide more information for their collection.”

While Larson is enthusiastically optimistic about the outcome of this unprecedented project, some scientists not affiliated with the study think the findings will only add to the existing mishmash of conflicting hypotheses. But that’s how science works: come up with an answer and you invariably end up with a lot more questions.

The ongoing search to understand where, when and how many times dogs were domesticated continues to be a topic of active scholarly exploration. Besides the millions of dog lovers who are curious about the roots of our affectionate and unusual cross-species relationship, substantial scientific issues are at stake, issues that may profoundly alter the future of evolutionary theory.

Read about new developments.

Good Dog: Studies & Research
Dog-Directed Speech
Puppies are most responsive to this type of talk

Baby talk may make grown-ups sound ridiculous to many people, but that doesn’t take away from its value. Extensive research has shown that human infants are better able to learn language when we talk to them using higher pitches and at a slower speed than when we talk to other adults. This style of communication is called “infant-directed speech”, and it’s natural for many folks to slip into it when addressing young individuals, especially those who are not yet verbal.

A new study called “Dog-directed speech: why do we use it and do dogs pay attention to it?” suggests that the same principle may be operating when humans speak to dogs—another of our social partners who don’t fully understand our language. People tend to talk to their dogs in a way that is similar to the way they address children. There may be value in this “dog-directed speech” as well.

This study investigated the behavior of two species, and reported a major finding about each of them. On the human side, only women were studied, and researchers found that they used dog-directed speech with dogs of all ages, but used higher pitches when they were talking to puppies than when addressing fully grown dogs. For the canines, this worked out well based on their age-related responses to the way we talk to them. Adult dogs were equally responsive to normal speech and dogs-directed speech. Puppies, however, became more engaged when addressed with dog-directed speech than when the women spoke to them as they normally talk. Specifically, it was the higher pitch in the dog-directed speech that influenced how attentive puppies were.

There are many questions that flow naturally from this study and its intriguing results. Do men talk to their dogs with higher-pitched, slower speech patterns, and does the age of the dog influence the degree to which they do it? Do dogs who look more juvenile because of larger eyes, shorter muzzles and bigger heads elicit dog-directed speech more than dogs who have a more mature look? Does dog-directed speech facilitate language learning in dogs as it does in human babies?

Do you talk to your dog using a different speaking style than the one you use for adult humans?

Good Dog: Studies & Research
Genes Underlying Social Behavior in Dogs
The same genomic regions affect human social behavior

The remarkable social abilities of dogs include the many ways that they are able to interact with humans. Dogs seek out humans for food, companionship, assistance and information. They have evolved these social skills throughout their recent evolutionary past because of the advantages of communicating and cooperating with people. Genetic changes in the domestic dog over thousands of years are the source of these behavioral changes, but there remains a lot of variation in both canine genetics and canine social behavior.

A recent study (Genomic Regions Associated With Interspecies Communication in Dogs Contain Genes Related to Human Social Disorders) investigated behavioral and genetic variation in hundreds of Beagles with similar upbringing and similar previous experiences with humans. Researchers studied the dogs’ social behavior by presenting them with an impossible task. Dogs were given a container that held three treats, but only two of them were accessible to the dog. The third treat was impossible for the dog to obtain. Using video, researchers quantified the time dogs spent looking at the people in the room with them, approaching them, and being in physical contact with them. Different dogs showed different tendencies to seek human interaction when they faced an unsolvable problem.

To investigate possible genetic sources of this behavioral variation, the scientists used a process called GWAS (Genome-Wide Association Study). Basically, this means that a large number of parts of the entire DNA of each dog were examined to discover potential genetic variants that were associated with the social behavior. This study shows a strong genetic aspect to differences in human-directed social behavior by dogs. Researchers found multiple sections of DNA that were associated with differences in social behavior. In some cases, specific alleles (gene variants) were strongly associated with the tendency to seek out humans for physical contact.

Interestingly, the genes associated with variation in dog behavior in this study have been found to be related to various behavioral issues and social behavior complexes in humans. Specifically, autism, bipolar disorder and aggression in adolescents with ADHD (Attention Deficit and Hyperactivity Disorder) are all variations in human behavior whose genetic contributions come at least in part from the same areas of DNA that influence human-directed social behavior in dogs. This suggests that dogs may be an appropriate and valuable model for studying these aspects of social behavior in people.

 

Good Dog: Studies & Research
Studying Our Relationships with Dogs
How to approach future research

“Yes, that’s just how it is with my dog, too!”

“Everybody knew that before reading about it.”

“I figured I wasn’t the only one who felt that way about my dog.”

“Obviously.”

These are common responses to stories about the many research papers investigating the relationship between people and dogs. Most of us read the latest scientific findings with a great sense of happiness and validation. Our relationship with dogs is very much like our relationship with our children? Yep. Our dogs consider their guardians to be extra special and emotionally important? Whew, thought so. Our attachment to our dogs provides us with many benefits? Duh. Being a helicopter parent does not cause the damage to fur kids that it can to human kids? Yay!  Gazing into our dog’s eyes can enhance the feelings of true love between us? Awww.

It’s exciting that there has now been enough research into attachment between people and dogs and the bonds they have for one another to prompt a review paper to suggest where to go from here. The recently published “Measuring dog-owner relationships: Crossing boundaries between animal behaviour and human psychology ” summarizes what we know and discusses what should be studied next as well as how. That means we can all happily anticipate more revelations that will further confirm the many details about what we know: Humans and dogs are close in wonderful ways that benefit us both. In the introduction to the paper, the authors say, “In this review, we propose that the next step in anthrozoology [study of interactions between humans and other animals] research is to use all the potential information within attachment theory, to reveal whether or not different types of relationship styles exist among different dog-owner dyads and how they might be identified. Furthermore, we give suggestions for which factors may contribute to the development of different attachment styles in dogs, hence deserving more attention in future studies of the dog- human relationship.” What this means is that there is a wealth of information about relationships between humans and the styles of connection that people have with one another that can be used to inform future research on the ways that dogs and people forms bonds to one another.

Some suggestions that these authors have are to focus on both dogs and people simultaneously rather than just one side of the relationship. They also recommend investigating physiological as well as behavioral responses to situations (such as separation and reunions) that are often the focus of attachment studies. They encourage addressing both the attachment style of individual dogs and the caregiving style of individual people to help pairs avoid any conflicts that have plagued them in the past and to help them form the best, most positive relationships in the future.

What are you most interested in knowing about the science of your relationship with your dog?

News: Guest Posts
Proof that Dogs Were Our Ancient Hunting Partners
Museum replication featuring Jōmon warriors hunting with dogs A recreation of a Jōmon hunt with dogs. Niigata Prefectural Museum of History

Here at The Bark we have long promoted the theory that from the very start of our long relationship with dogs, they were our valuable partners. And, our evolutionary pathways most likely crossed along game trails rather than, as some contend, on ancient garbage mounds. Or as Mark Derr, our former science editor, and author of How the Dog Became the Dog, explained to us, “The premise I start with is that, in many ways, dogs are an evolutionary inevitability. As soon as humans and wolves encountered one another on the game trails, they struck up a relationship, and they’ve been at it ever since.” 

Well, it looks like recent research into prehistoric Japanese graves proves, at least, that dogs were indeed our long-time hunting companions. In this fascinating study written by Angela Perri recently published a fascinating study that proves just this. This line of inquiry started when she was a grad student at Durham University in the UK. As David Grimm writes in Science:

“She wanted to get a sense of how dogs may have aided early humans in taking down game, so she did her best to approximate the activity: In 2011, she joined a group of Japanese businessmen on a wild boar hunt in a dense forest near Hiroshima. ‘It was terrifying,’ says Perri, now a zooarchaeologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. ‘The boar sound like a train. They’re very aggressive, and they have big tusks. At any moment, one could come charging at you.’”

But the biggest takeaway she got was just how impressive the dogs were during this hunt. Not only did the 5 Bloodhounds and Shiba Inus help to track down the prey, but they also warned the humans when the boars were nearby.

That got Perri interested in investigating Japanese research papers for anything about dogs and the Jōmon culture—hunter-gatherers from 16,000 to 2,400 year ago. They lived in the northern islands with a cold climate filled with large terrestrial megafauna of the Pleistocene, like Naumann’s elephants and Yabe’s giant deer. But during the Holocene, 10,000 to 12,000 years ago, there was a climatic warming displacing the larger animals with smaller, quicker ungulates like sika deer and wild boar. As Perri notes in the Antiquity paper, “This environmental shift … led to the creation of new exploitation niches for Jōmon foragers, including important variations in plant availability, coastal resources and terrestrial prey species.”

Perri’s research has involved studying dogs as “hunting technology,” and as she noted, “A hunting partnership between dogs and humans has long been postulated in the archaeological literature, with some researchers suggesting that such a collaborative alliance was the basis for the initial domestication of dogs. She points out that, “Dogs are an important, and in some cases indispensable, hunting aid for many modern forager groups, as they probably were for foragers in prehistory.” And explains that, “Injured deer often run, leading hunters on long chases, and wild boar can be aggressive and quickly learn to evade capture. Hunting dogs mitigate these factors by tracking blood trails, forcing game into vulnerable positions (e.g. in water) and holding prey until the hunter can make the final kill.”

Perri was familiar with the significance that dogs had with many ancient cultures, and how the ethnographic record has confirmed their importance and the revered status many of the dogs obtained, which often was displayed in the manner they were buried in “remarkably human-esque ways, often with grave goods and markers.”

She performed a comprehensive survey of Japanese archaeological literature, and found that the Honshu Jōmon did bury their canine hunting partners in shell middens, same as they did with humans. And found over 110 canine burials from 39 archaeological sites. “They were treating their dogs the same way they treated their human hunters.” And, “Like people, the dogs (which may have resembled Shiba Inus) were placed singly and appear to have been arranged in particular postures. ‘They looked like they curled up and went to sleep,’ Perri notes. Some had suffered what appeared to be hunting injuries—broken legs and teeth—and many of their bones had healed, suggesting people had taken care of them. Some were also found with grave goods, like shell bracelets and deer antlers.” Their ages ranged from newborn to over 12 years old. While the prehistoric puppies weren’t certainly valued as hunters, she noted that “the ethnographic record shows that puppies in hunter-gatherer groups are often valued for their potential as future hunting partners.”

Along with the burials themselves, Perri found that the “importance of hunting dogs in this region is also demonstrated by the numerous dog-shaped clay figures (dogu), including a set that features a dog barking at three wild boar.” Or, “One Yayoi representation of dogs is found on a ceremonial bronze bell (dotaku) depicting a number of scenes, one of which is a boar surrounded by a hunter and a pack of dogs.” As shown here:

A 2500-year-old bronze bell depicting a Jōmon hunt with dogs. Image courtesy of Tokyo National Museum (http://www.tnm.jp/)

 

Perri concludes that while dogs were an integral part of the ancestral forest hunting culture, once an agricultural subsistence culture took over, the dog burials stopped as well.

As Grimm noted in his article and quotting Melinda Zeder, an archaeozoologist at the Smithsonian Institution National Museum of Natural History, “it may be a disparity in loyalty. “Humans were a bit of a fair-weather friend—we were not as reliable as they were,” she laughs. “We could do to be a little more doglike.” We couldn’t agree with that sentiment more.

Good Dog: Studies & Research
Comparison of Risk-Taking in Dogs and Wolves
The influence of each species’ feeding ecology
Comparison of Dogs and Wolves

Humans tend to be risk-averse, which is often illustrated by our decision when offered either $100 or the opportunity for a 50-50 shot at receiving either $200 or nothing. In general, humans go for the sure thing. We are not, as a species, risk-prone, or we would gamble on the shot at getting the bigger payoff.

It turns out that a number of studies across a broad range of species have shown that how a species responds to risk is predictable based on their feeding ecology. Animals who depend on erratic, ephemeral food sources, such as meat that they hunt or fruits that are patchy and only ripe for a brief time, tend to be risk-prone. They are willing to gamble on the big payoff. Species that eat diverse types of food or food that is more reliably available, such as vegetation, are risk-averse.

Some of our primate relatives are like us, and some are the opposite. For example, bonobos and lemurs (who both eat a very diverse diet that is mainly vegetarian) are risk-averse like us, choosing a sure thing of lower value over a chance at something better. Chimpanzees and capuchin monkeys—both meat and patchy fruit eaters—are different, being risk-prone and choosing the option that may yield a big reward but could leave then empty-handed. This pattern has appeared in closely-related species birds, too, where those who eat insects are risk-prone, while species who eat seeds are risk-averse.

Scientists haven’t fully explored how widespread this pattern of feeding ecology predicting risk-taking behavior is, but wolves and dogs are an interesting test case. These two species diverged quite recently in an evolutionary sense, but their feeding ecologies differ greatly. Wolves are primarily hunters and dogs are mainly scavengers. Hunting has a high failure rate, but the rewards of a big kill are enormous. In contrast, the source of food for the vast majority of dogs worldwide is human refuse, which tends to be available far more regularly.

In a recent study called “Exploring Differences in Dogs’ and Wolves’ Preference for Risk in a Foraging Task” scientists investigated whether wolves and dogs conform to the pattern seen across so many other species. Based on their different feeding ecologies, they predicted that compared with each other, wolves would be risk-prone and dogs would be risk-averse. The study was done at Wolf Science Centre in Austria, using dogs and wolves who were raised and live at the facility and have had the same overall experiences there.

The subjects of the study were trained to choose either a bowl that contained a dry pellet of food or a bowl that had a fifty percent chance of containing a piece of meat and a fifty percent chance of holding a stone. After each choice, the subject was given the contents of the bowl. All the wolves and dogs in the study were subject to tests to confirm that they understood the choice they were making and also to confirm that they preferred the meat to the dry food pellet.

The researchers found that the pattern of risk-taking seen in other species also applied to wolves and dogs. As expected, wolves were more risk-prone than dogs. However, there is more to this study than that simple conclusion. Wolves learned the system faster than the dogs, and the researchers acknowledge that they may have understood it better than the dogs. Additionally, dogs’ preference for the meat versus dry food pellet was not as strong as it was for wolves. Therefore, the risk of losing out and getting nothing for the chance to get something only a little better than a food pellet may not have been worth it to dogs. There was greater variation among individual dogs in risk-taking strategy compared with wolves, who were more similar in their choices, so it’s possible that there are dogs who are risk-prone as well as dogs who are risk-averse. (Dogs made the risky choice from 38 to 76 percent of the time, while wolves took the risky option 70 to 95 percent of the time.)

Overall, despite the conclusions made from the data in this study, direct comparisons of the choices made by these two species may require further study. It would be very interesting to learn more about decisions to take risks by dogs and wolves in a study with more than seven of each species, though I realize possible subjects for a study such as this are limited. It would also be fascinating to know about the decisions foxes and coyotes would make if presented with the same choices. Comparative research that include dogs as one species among many allow us to learn a great deal about how their evolutionary history and ecology have affected their behavior. It’s one of many ways that we can deepen our understanding of the animals who share our homes and live in our hearts.

Culture: DogPatch
Q&A with Author Frans de Waal
Are We Smart Enough to Know How Smart Animals Are?
Are We Smart Enough to Know How Smart Animals Are?

In Are We Smart Enough to Know How Smart Animals Are? Frans de Waal presents a fascinating history of the study of animal behavior and cognition. De Waal, who says his love of animals dates to his childhood, is a worldrenowned primatologist and ethologist and director of the Living Links Center at the Yerkes National Primate Research Center. We asked him to shift gears and give us his take on the canine mind.

Bark: Konrad Lorenz (co-founder of your field) wrote Man Meets Dog in 1954. And while it is still one of the best, if slightly flawed, books on canine behavior, why did it take so long for ethologists, and other researchers, to to study dog behavior?

Frans de Waal: Dogs were (and are) considered imperfect subjects of study because they are “unnatural.” Many ethologists, including Lorenz, feel that natural behavior under naturalistic conditions is what we should focus on, and the dog is a product of artificial breeding. Lorenz liked all animals, however, and so couldn’t resist describing his dog stories, and we should all be grateful.

Clearly, the dog is a mammal with many typical mammalian tendencies, so now scientists are finally seeing that the fact that they are domesticated also has advantages. For example, they are eager to work with us, they are generally not dangerous, they are smart, they have empathy. Lots of great things can be done with them. And they are easier to work with than other large mammals, such as apes and dolphins.

Bk: Can you give an example of how other species, including dogs, demonstrate empathy?

FdW: American psychologist Carolyn Zahn-Waxler sought to determine at what age children begin to comfort family members who sobbed or cried “ouch.” It turns out that children do so at one year of age. In the same study, Zahn-Waxler accidentally discovered that household dogs react similarly. Appearing as upset as the children by the distress-faking family members, the dogs hovered over them, putting their heads in their laps with what looked like great concern. This work has recently been repeated in different studies, more focused on the dogs themselves, and it is clear that these animals show empathic concern for humans.

The ancestor of the dog, the wolf, probably behaves the same. If “man is wolf to man,” as Thomas Hobbes liked to say, we should take this in the best possible way, including a tendency to comfort the whimpering and help the needy. This insight, of course, would undermine much of political philosophy based on Hobbes’ dog-eat-dog view of nature.

Bk: Do you think human bias has played a part in some of the canine cognitive studies?

FdW: At first, dogs were rated as more intelligent than even apes and wolves because they followed the direction of human pointing (at a bucket with food), whereas apes and wolves ignored human directions. Then it was found that wolves raised in a human home will act more like dogs, following human pointing, suggesting that the earlier failures with wolves were probably due to lack of bonding and attention. The same probably applies to the apes. Now, dogs are seen not just as smart but rather, as finely in tune with the species that bred them.

They have a special bond with us, as also reflected in the oxytocin studies, which show that human-dog contact increases this “cuddle” hormone in both. The dog is perhaps the only animal that performs at its peak when tested by humans, whereas many other animals are not so into us, hence need to be tested in different ways. This is yet more proof that cognitive testing of animals always needs to take into account what kind of animal we are dealing with: we need to find the most species-appropriate way.

Bk: In contrast to behaviorism’s reward/ punishment model, ethology views animals as “seeking, wanting and striving.” Why do you feel the latter is a more productive way to look at animals?

FdW: The behaviorists (followers of B. F. Skinner) totally overlooked natural animal tendencies. Trying to explain all behavior on the basis of reward and punishment, they could not explain why you can train a dog to fetch, but not a rabbit or a goat.

Predators are obsessed with small moving objects, which we see every day in our dogs as well as cats. Their interest sets up a learning situation where they are going to absorb many lessons about how to catch these moving objects, how to trick them, how to outsmart them. Dogs eagerly learn all of those things.

Reward and punishment are only small parts of the story; their natural hunting instinct is, in fact, the driver of the process. This is where behaviorism failed. It had some good ideas, many of them applicable to animal training, but its perspective was far too narrow as it lacked attention to natural tendencies and the evolution of behavior.

Bk: Why do you think Darwin used dogs to illustrate emotional continuity?

FdW: Darwin was a dog lover, and he knew that to get his message across about the continuity between human and animal emotions, the dog would be the easiest way to communicate. Darwin mostly worked on the expression of emotions (it’s hard to know what animals feel, but we can at least document how they signal various states, such as fear, submission, anger, affection). Of course, the dog is very expressive with its postures, facial expressions, tail-wagging, growling and so on. Darwin knew that most people could relate to all of this, and would have more trouble if he described other species that people have less exposure to.

Bk: In terms of an evolutionary advantage, how important is it for a species to have self-awareness, or theory of mind?

FdW: These capacities require large brains. In terms of recognizing oneself in the mirror or understanding what others know, the champion species are apes, dolphins, elephants and perhaps also the corvids (crow family). This doesn’t mean that dogs lack them. They probably have similar understanding, but not as fully expressed.

The more complex the societies of a species, the more demands there are on cognition, and perhaps canines do not need social understanding at the level of an ape or dolphin. I feel we need to judge animals on what they are good at and what they need to know to survive. In this regard, canines have lots of specialized skills, often related to their sense of smell, their pursuit of prey, their need for tight cooperation and so on. This is where we should test them out, and probably find remarkable skills.

Bk: Clearly, emotions are important to the understanding of behavior; how do they relate to and inform one another?

FdW: In my book, I left emotions out on purpose because I felt it would muddle things. But there can be no studies of cognition without attention to the emotions, and vice versa. The two go hand in hand. In our famous capuchin monkey experiment with the grape and the cucumber, for example, you can see not only that the monkeys judge what they get relative to what others get, but also their strong emotional response. You cannot study the one and ignore the other.

Good Dog: Studies & Research
Dogs Understand Our Words and Intonation
What you say and how you say it both matter
Dogs Understand Our Words - Study with MRI

Humans use both words and the intonation of speech to decipher the meaning of language, and it turns out that our dogs do, too. In a research paper called “Neural mechanisms for lexical processing in dogs” scientists investigated how dogs process the meaning of language. They found that dogs’ brains have even more in common with humans’ brains than previously thought. (It’s not clear when we will collectively stop being surprised by this, but I hope we always remain excited about new evidence to explain why we feel that dogs are kindred spirits.)

In this study, dogs who have been trained to remain still while their brain activity is recorded listened to recordings of their trainers talking. There were four types of recordings: 1) words of praise spoken with intonation typically associated with praise, 2) words of praise spoken with a neutral intonation, 3) neutral words spoken with intonation typically associated with praise, and 4) neutral words spoken with a neutral intonation.

Researchers analyzed the brain activity of the dogs in response to each of the recordings, and came to several conclusions about the way that dogs respond to words and the intonation of human speech. The dogs processed the vocabulary in the left hemisphere of their brains, which is where humans also process the meaning of words. The dogs processed the intonation of the words separately, in a different region of the brain. Just as humans do, dogs processed the intonation of human speech in the right hemisphere of their brain. Dogs also process sounds that convey emotion without words in this same region of the brain’s right hemisphere.

Dogs process both words and the intonation of human speech to decipher meaning. Just as humans do, they process these two aspects of speech separately, then integrate them to determine the full meaning of what was said. Only the praise that was spoken like praise—higher pitched than normal speech and with more variation in pitch—activated the reward centers of dogs’ brains. Though they may understand words of praise said in any manner, it only makes dogs happy to hear us praise them when we do it with proper feeling.

This research does more than reveal yet another similarity in the way that human and dog brains process information. It also suggests that the ability to connect a word to a meaning did not develop with the evolution of spoken language. Rather, it is a more ancient ability that can be made use of in the context of the human-dog relationship to link specific sounds to specific meanings.

The take away messages from this research are that dogs process two parts of spoken language—words and intonation—the same way that humans do and if you want to make your dogs happy, you have to praise them like you mean it!

Good Dog: Studies & Research
How and Why Dogs Play Revisited: Who’s Confused?
Beliefs do not substitute for data

Watching dogs play is very exciting, and there has been a lot empirical research on how and why dogs (and other animals) engage in this activity with boundless zeal. A number of people have asked me to comment about dog play after reading this section in a new book by Raymond Coppinger and Mark Feinstein called How Dogs Work. So, I decided to do so.

The authors begin their chapter 9 on play by claiming, “Hundreds of scientific papers have been written on the subject of ‘play’ behavior—an activity for which dogs are, of course, famous.” Recognizing that there is a solid and growing literature on play—there’s really no reason to put the word play in square quotes—I assumed that what followed would be a detailed review of this research, but rather, what I discovered was a disjointed discussion of play and not an in-depth review of the scientific literature. Instead, the authors offer their own unpublished observations and the results of unpublished student projects, all of which are impossible to assess. 

Do dogs and other animals actually play? Coppinger and Feinstein write that they put the word play in scare quotes because “in spite of the fact that people feel like they know it when they see it, it’s not at all obvious that play is a unitary ‘thing-in-itself’ that can easily be characterized, let alone explained in evolutionary terms.” No one I know who has spent years studying play would argue that play is a “unitary ‘thing-in-itself’,” nor would they agree that play cannot be explained “in evolutionary terms.” Indeed, some of the references the authors include show there are a number of highly plausible evolutionary explanations (and the University of Tennessee’s Gordon Burghardt, who has studied comparative aspects of play for many years and wrote The Genesis of Animal Play, provided the Foreword for Coppinger and Feinstein’s book). 

Why do animals play? Briefly, various theories have been offered about why animals play, and there’s no one explanation that fits all examples of animal play. Detailed comparative data show play is important in social development, physical development, and cognitive development. And, neurobiological research strongly suggests play can be pleasurable and fun and animals may simply play because it feels good, “for the hell of it.” Indeed, many researchers are taking fun seriously, and the 25th anniversary issue of the journal Current Biology was devoted to the biology of fun with many play researchers weighing in on the topic. Coppinger and Feinstein write, “We agree that there is good reason to believe that animals derive pleasure from play - indeed they do from all of their motor activities.” (my emphasis) While animals might derive pleasure from play, eating, and sex, it’s difficult to argue they feel good running from competitors or predators, but the necessary research has not been done. 

Based on an extensive review of available literature, my colleagues Marek Spinka, Ruth Newberry, and I proposed that that play functions as training for the unexpected by increasing the versatility of movements and the ability to recover from sudden shocks, such as the loss of balance and falling over, and to enhance the ability of animals to cope emotionally with unexpected stressful situations. To obtain this training, we suggested that animals actively seek and create unexpected situations in play and actively put themselves into disadvantageous positions and situations.

Comparative data from a wide range of species support this hypothesis. And, while it is difficult to test these ideas in the field, a study of mountain goat kids by Rachel Théoret-Gosselin, Sandra Hamel, and Steeve D. Côté called “The role of maternal behavior and offspring development in the survival of mountain goat kids“ showed that “play behaviors could enhance the emotional resilience to stress not only for unpredicted events but also in stressful group situations because play could reduce aggressiveness in gregarious species.” More field data are needed and this study is an excellent example of what needs to be done.

The play bow: Are dogs really confused when they play and what does this mean?

The authors also dismiss the detailed work that has been conducted on the play bow, a highly ritualized and stereotyped action by which animals signal their intention to play (please see accompanying image). When dogs and other animals bow they crouch on their forelimbs, raise their hind end, and occasionally wag their tail and bark. Coppinger and Feinstein write, “But we wonder if the so-called play bow in fact really has any adaptive, let alone cognitive, significance.” A good deal of very detailed research has been conducted on the bow by my research group and also by Barbara Smuts and her students that clearly supports the claim that bows are adaptive and have cognitive significance (please also see along with Mechtild Käufer’s excellent book called Canine Play Behavior: The Science of Dogs at Play and a comprehensive review essay by Elisabetta Palagi and eight other play experts called “Rough-and-tumble play as a window on animal communication“). The abstract for this excellent evidence-based and extremely significant up-to-date essay reads: Rough-and-tumble play (RT) is a widespread phenomenon in mammals. Since it involves competition, whereby one animal attempts to gain advantage over another, RT runs the risk of escalation to serious fighting. Competition is typically curtailed by some degree of cooperation and different signals help negotiate potential mishaps during RT. This review provides a framework for such signals, showing that they range along two dimensions: one from signals borrowed from other functional contexts to those that are unique to play, and the other from purely emotional expressions to highly cognitive (intentional) constructions. Some animal taxa have exaggerated the emotional and cognitive interplay aspects of play signals, yielding admixtures of communication that have led to complex forms of RT. This complexity has been further exaggerated in some lineages by the development of specific novel gestures that can be used to negotiate playful mood and entice reluctant partners. Play-derived gestures may provide new mechanisms by which more sophisticated communication forms can evolve. Therefore, RT and playful communication provide a window into the study of social cognition, emotional regulation and the evolution of communication systems.

The so-called play bow. Based on an unpublished student project in which “Border collies were confronted with normal and drugged roosters”,  Coppinger and Feinstein believe that the “so-called play bow” is a posture assumed by an animal confused by its next move. They write, “... the play bow occurs when an animal is in a temporarily indeterminate state ... In short, the ‘playing’ animal is in conflict about its next move - and the play bow in fact looks just like a combination of multiple conflicting behavioral shapes.” The authors ignore detailed research that shows how play bows are extremely stereotyped (they are what ethologists call a modal action pattern), they vary in shape and duration depending on where they are performed in a play bout, and they allow a dog to perform a wide variety of movements from this posture. There are no data that support their belief and the student’s data are impossible to assess. And, it’s not clear at all why they refer to the “so-called play bow,” when many researchers have studied it and concluded, based on substantial data, that it is indeed used almost exclusively in the context of play both as a play invitation signal and also to maintain the play mood. 

Let’s briefly think about what it means when a dog or other animal is confused, because every definition I can find indicates that there have to be cognitive and emotional underpinnings. In the case of dog-dog play, a simple view would be that Harry (a dog) wants to play with Mary (another dog) and that Harry isn’t sure what to do so he carefully pays attention to what Mary has done and is doing, and tries to factor this information into what she is likely to do in the future. In essence, Harry is pondering if he chooses to do “X” or “Y,” what will Mary do (and, of course, vice versa). Because play is indeed a hodge-podge of various actions, a kaleidoscopic behavior, on the authors’ view, Harry is confused, and to overcome his confusion he performs play bows.

There are no data that support the belief that dogs are confused when they play, however, there are data that show that there is a good deal of rapid of thinking and feeling on-the-run based on what Harry thinks and feels Mary is likely to do during the on-going interaction (and vice versa). These sorts of interactions make it clear that play is also a good place to observe and to study what researchers call a “theory of mind,“ because Harry and Mary need to pay very close attention to what each has done and is doing, and how that will influence what she or he is likely to do in the future (for further discussion please see Alexandra Horowitz’s essay called “Attention to attention in domestic dog (Canis familiaris) dyadic play“). There is a good deal of mind-reading going on here as Harry and Mary make careful and rapid assessments and predictions of what their play partner is likely to do. 

The cognitive and emotional underpinnings of “being confused” are rather rich, and do not lend themselves to simple mechanistic explanations that are favored by the authors. Available and ample data for a number of different species show there are predictable rules of play that cross species lines, namely, ask first, be honest, follow the rules, and admit you’re wrong. This is why play is so exciting to engage in and also so much fun to watch and to study. And, this is also why play among young and old dogs only rarely escalates into injurious aggression, although the authors recall an instance when play among four-week-old Border collie littermates was fatal and use this observation to claim that play “can itself cause significant harm” (p. 165). Indeed, Shyan, Fortune, and King (2003) reported that fewer than 0.5% of play fights in dogs developed into conflict, and only half of these were clearly aggressive encounters. Their data agree with our own observations on wild coyotes and free-running dogs at play.

Behavioral variability. Another example of a claim that is countered by available data centers on behavioral variability in young dogs and wolves. Coppinger and Feinstein write, “When we observe wolves, we see a similar picture. Wolf puppies are often noticeably more robust and varied in their play routines than dogs of the same size and age. This means, according to our hypothesis, that they should have more available motor patterns than the dogs do. That is in fact the case.“ (my emphasis) However, they offer no data. 

Along these lines, years ago Robert Fagen, another play expert and author of the classic book Animal Play Behavior, analyzed the sequential variability of play and aggression in young dogs (beagles), wolves, and coyotes using data my students and I collected, and discovered that social play in the beagles was more variable than social play in wolves and coyotes of the same age (and coyote play was more variable than wolf play). These data were published in an essay I wrote with John Byers (“A critical reanalysis of the ontogeny of mammalian social and locomotor play: An ethological hornet’s nest,” in K. Immelmann, G. W. Barlow, L. Petrinovich, and M. Main, Eds., Behavioral Development, The Bielefeld Interdisciplinary Project. New York: Cambridge University Press, pp. 296-337, 1981) that the authors list in their reference section. And, we also found that young beagles and wolves shared the same basic ethogram and number of motor patterns. Perhaps working dogs such as Border collies are different from beagles and other dogs, but we really don’t know if this is the case. 

The way in which the authors routinely dismiss a wealth of detailed research on animal play is characteristic of much of their book, that is essentially a tapestry of criticism using stories and unpublished projects in lieu of published data. It’s easy to see how one might walk away feeling that just about everyone else is wrong about dog behavior, cognition, emotions, and consciousness, and much of the research that has been done can be tossed into the garbage because it’s merely debris. 

All in all, the one-sided assault on the ever-growing literature in the growing field called cognitive ethology (the study of animal minds) fails. How Dogs Work does not really tell us how dogs work, but rather provides an extremely narrow view of mainly working dogs as machines. I find the topic to be of great interest and am always eager to learn more about why some people favor reductionist and mechanistic accounts to explain the behavior of complex sentient beings (see, for example, Sara Shettleworth’s book, Fundamentals of Comparative Cognition). However, How Dogs Work doesn’t convince me that the authors’ over-arching views are tenable. Beliefs don’t substitute for data that have been reviewed by peers, and there are plenty of data that are readily available. 

All in all, we really know far more than the authors offer, and for numerous wide-ranging and critical discussions of many different aspects of dog behavior I suggest  Domestic Dog Cognition and Behavior: The Scientific Study of Canis familiaris edited by Alexandra Horowitz, Adam Miklosi’s Dog Behaviour, Evolution, and Cognition, The Social Dog: Behavior and Cognition edited by Juliane Kaminski and Sarah Marshall-Pescini, and Mechtild Käufer’s Canine Play Behavior: The Science of Dogs at Play. For more on play I highly recommend the excellent and comprehensive review article by Elisabetta Palagi and her colleagues called “Rough-and-tumble play as a window on animal communication“ and (in addition to the references above) Sergio Pellis and Vivien Pellis’ The Playful Brain: Venturing to the Limits of Neuroscience.

What’s so incredibly exciting about the study of play behavior and the cognitive and emotional lives of dogs and other animals is how much we’re learning about how individuals negotiate challenging and complex social and non-social situations by carefully analyzing what’s happening and by using hard-wired actions when needed (for example, when they need to do the right thing instantaneously or the first time they are faced with a specific situation and there’s no room for error), along with behavior patterns that require careful thought and flexibility motivated by what individuals are feeling about the situation in which they find themselves.

Please stay tuned for more on dog behavior, cognition, and emotions, because there is a lot of research being done by research groups around the world, and we still have a lot to learn. Dogs are amazing sentient beings who challenge us in many different ways.

I thank a number of people for help with this essay.

Note: In a number of email messages I've been asked if I knew what happened to the 1000’s of sled dogs dogs for whom Dr. Coppinger was responsible. On page 25 we’re told, “Some four thousand dogs ‘went through the yard’” when “Ray spent fifteen years breeding and training dogs that pull sleds.” I have no idea what happened to these dogs, but according to some people I consulted, this is an incredibly large number of dogs, an average of around 267 a year. 

Wellness: Healthy Living
Study Finds Declining Fertility in Male Dogs
Toxic chemicals also found in dog food

A long-term study conducted in Britain has found that male dogs are losing fertility, and that exposure to environmental chemicals (ECs) that have leached into the environment may be to blame.

The dogs—Labradors, Border Collies, German Shepherds and Golden Retrievers bred to aid the disabled—made an ideal group to explore the larger question of a decline in human semen quality that has been occurring since long before this study.

This twenty-six year long study, 1998-2014, was conducted by Richard Lea and colleagues at Nottingham University’s school of veterinary medicine. They collected annual samples of semen from dozens of dogs, all from the same breeding program, all healthy and well cared for. Each year, the same problem recurred; a 2.4 percent dip in sperm motility, that is the ability to swim in a straight line. In addition to monitoring semen quality, they analyzed health records, finding an increase in cryptorchidism, a condition in which the testicles fail to extend normally to the scrotum. Over the same years, fewer male pups were born than females, also there was an increase in fetal and prenatal female mortality.

And, lurking in the samples of semen and testicles of dogs obtained from neutering, it found ECs—chemicals that tamper with hormones. The chemicals include polychlorinated bisphenol (PCB), a compound banned in 1977, and diethylhexyl phthalate (DEHP). PCBs don’t readily break down while phthalates are common in a wide number of products, from cosmetics to detergent. Both chemicals are associated with fertility issues and birth defects.

In human babies, exposure to chemicals has been linked to faulty development of semen quality and cryptorchidism. According to the study, such reproductive problems often cluster in geographical areas, and so are suspected of having a common cause; exposure to hormone-disrupting chemicals is “thought to be the initiator.” To explore the same possibility in dogs, chemicals were measured in canine testes and semen taken from the same geographical area where the study took place.

Both chemicals “perturbed sperm viability, motility and DNA integrity in vitro.” The researchers concluded that the direct effects of chemicals on sperm “may contribute to the decline in canine semen quality” that parallels that in humans.

“Why the dog?” said Dr. Lea. “Apart from the fact that it is a great population of animals to work with, dogs live in our homes, they sometimes eat the same food, they are exposed to the same environmental contaminants that we are, so the underlying hypothesis is that the dog is really a type of sentinel for human exposure.”

The same ECs were found in a range of commercially available dog foods. DEHP and PCB153, “were detected in adult dog testes and commercial dog foods at concentrations reported to perturb reproductive function in other species.”

While the brands were not named, they are reported to be both wet and dry forms sold worldwide. The scientists don’t know how the chemicals made it into the food, but since they are not deliberate additives, they may have leached from the packaging or processing sources.

These overall findings are troubling, but they also noted that: “Amongst the dry dog food samples, one sample designed for puppies (1 to 24 months of age) had higher concentrations … relative to the other samples tested.”

Plus, while the researchers cannot say the dog food is a direct source of the ECs, the New York Times reports that "Dr. Lea said it was probably a major one." 

What is known is that the chemicals wound up in dog’s testicles, where they messed with sperm motility and viability. “This may be a way by which environmental chemicals directly affect male fertility.”

While the dogs in the study were still able to reproduce, it’s hardly reassuring that, once more, the dogs who share our homes also share our diseases, unwittingly, acting as the “canary in the mine” for us.

 

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